I agree that the notion of " reproductive sex" as a transitory life phase which tracks gamete production makes sense - it's the position of Paul Griffiths (although he, somewhat unfortunately, labels this as "biological sex"):

https://philarchive.org/rec/GRIWAB-2

As Griffiths (and the article you cite) notes, that conception is distinct from and does not bear upon how we define and use "sex" as a social category.

The "fatuous synecdoche" I'm talking about is the attempt to conflate that very narrow sense of "sex" qua gamete production with the broad senses in which the word "sex" is used beyond biological literature.

It's clearly an abuse of science to cite "anisogamy" (something that no one is debating) in support of a pretense that the mutable characteristic of gamete production somehow maps to an immutable essence that inevitably dictates social organization. This is just the use of scientific vocabulary to provide a pretext for declaring that trans existence is nonsensical and therefore eradicable. As seen in the enactment of despicable laws that are intended to enforce that sadly truncated view of humanity.